Category 12 years to 15 years : presentation of experiments on light.


4th Junior High School in Petroupoli, Greece: Light, color and heat


Imagine that it is 40 degrees outside. How do you stay cool? What kind of clothing do you wear?

Can you think of any instances that the color of an object makes a difference in how hot it gets in the sun?


In 4th Junior High School in Petroupoli, we tried to approach


How the color of an object


heat absorption

of light



OS Prezihovega Voranca Jesenice, Slovenia


From the shadow of a stick to the ....circumference of earth

Repetition of Eratosthenes Experiment

4th junior High School in Petroupoli, Greece



On the 20th of March 2015, the closest to the vernal equinox date, our school had calculated the circumference of Earth.

What we had done is use a cylinder of a map case (we call this a “gnomon”), measure its length, hold it vertical to the ground and measure its shadow at solar noontime, when the shadow is the shortest. Then we calculated the angle that sunrays hit the ground.





 Other schools that date, had the same procedure of measurements, too. We exchanged data with those schools and using in a method of three the difference of the angles of the sunrays to the ground, we calculated the circumference of earth.




We did this, because of the participation of our school in etwinning project Eratosthenes 2015, an ongoing etwinning project that celebrates its ten years of life.





 On March the 20th, 16 schools of this project had also measured their gnomons and shadows.


Matching our data with theirs, the most accurate calculation for our school, came from matching those of the French college Antonin Perbosc in Lafrancaice, France.




 The circumference of earth calculated as 39954 Km.




This is a repetition of Eratosthenes experiment, which originally took place 2200 years ago. Watching this video you'll get a description of it (click on the following picture):


And more vividly and precisely the mathematician’s part is explained in this one (click on the following picture):


 You can also repeat this experiment!

We are looking forward to exchange measurements with you!



College Antonin Perbosc, Lafran├žaise FRANCE


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